Typical crab traps consist of a generally cubical or rectangular enclosure made of wire mesh or of netting supported by a metal frame. These traps generally have one or more entryways which provide a way for crabs to enter the trap and which prevent their escape therefrom. Typical traps of this nature are well known and shown in U.S. Pat. Nos. 3,184,881; 3,373,523; and 4,184,283.
The crab entryways are often in the form of an inwardly-converging and upwardly-sloped tunnel through which crabs will crawl seeking bait located inside the trap. Typically, escape from the trap is prevented, or at least deterred, by either spacing the interior end of the entry tunnel some distance above the bottom of the trap so that entering crabs spill over into the trap in a known manner, or by providing a swinging gate at the opening which acts as a one-way door, or by a combination of both.
Examples of such swinging gates are shown by U.S. Pat. Nos. 2,530,449 and 3,678,612. The disadvantages of such swinging gates are well known and are prone to malfunction due to corrosion and other factors. The problems associated with hinged entry gates are thoroughly discussed in U.S. Pat. No. 4,184,283 which discloses an upwardly sloped, converging entry tunnel having a comb-like gate structure made of a plurality of resiliently bendable tines affixed adjacent the inner end of the entry tunnel. An upwardly-spaced entry opening, without a one-way gate, is often inadequate to retain trapped crabs because of the crab's natural tendency to climb upwardly.
The structure of virtually all crab traps requires that the trap be set on the ocean floor in an upright position. Crab traps that are cubically or rectangularly shaped are generally simply placed in the water in an upright position and allowed to sink to the bottom. U.S. Pat. No. 2,530,449, issued to E. L. Bush, discloses a crab trap having concrete weights along bottom edges thereof and an upwardly-extending bridle to which a retrieval line is attached. A completely filled crab trap can be very difficult to lift or pull through the water. Weights built into the trap add to the difficulty of lifting the trap through the water and in the handling of the trap on deck.